atwood



July 13, 1954 J. 5. ATWOOD PROCESS OF ABSORBING ETHYLENE IN SULFURIC ACID Filed May 29, 1952 KOWWwmniOu INVENTOR- JOHN S ATWOOD 1442 ATTORNEY Patented July 13, 1954 ,tsanz sr orric PROCESS OF ABSORBING ETHYLENE IN SULFURIC ACID John S. Atwood, Port Washington, N. Y., assignor to National Petro-Chemicals Corporation, a

corporation of Delaware Claims.

This invention is a new and useful process of absorbing ethylene in sulfuric acid to produce a mixture of mono and diethyl sulfates. The invention is applicable to those mixtures of inert gases and ethylene which are substantially free from higher olefins. The preferred raw material contains from 80 to 98% of ethylene although the process can be used with a gas containing as low as 30% by weight of ethylene. Such gases may be commercially produced by the cracking of natural gas followed by a rectification operation to separate a close out consisting principally of C-2s. It is preferable but not essential to rectify this mixture further to separate a close out consisting principally of ethylene.

The invention will be fully understood from the following description read in conjunction with the drawing which is a diagrammatic showing of apparatus in which the invention may be carried out.

Referring to the drawing, a gas stream which has been compressed to a pressure of at least 300 lbs. gauge and from which light fractions such as hydrogen and methane have been removed, is passed through pipe I controlled by valve 2 into the mid-section of a rectifying column diagrammatically indicated as 3. This column may be equipped with a reflux device (not shown) adjacent the upper end thereof and with a reboiler (not shown) adjacent the lower end thereof. Rectifying column 3 produces an overhead, consisting principally of C-2s, which is withdrawn through pipe 4, passing thence through control valve 5 into pipe 5 controlled by valves 1 and 8. Bottoms consisting of C-3s and higher is withdrawn through pipe H controlled by valve l2 for rccracking or utilization elsewhere. This overhead consisting principally of C-Zs and containing at least 30% by weight of ethylene may be passed directly through pipes 6 and 28 into the absorbers to be hereinafter described but is preferably passed at least in part through pipe 13 controlled by valve M into the mid-section of a second rectifying column diagrammatically indicated as I5.

Column [5 is also equipped with a reflux device (not shown) adjacent the upper end thereof and a reboiler (not shown) adjacent the lower end thereof. This column is adapted and operated. to produce an overhead consisting principally of ethylene. Preferredly this overhead contains from 80-98% of ethylene, remainder principally ethane. Bottoms from column l5 consisting principally of ethane with some ethylene is withdrawn through pipe it controlled by valve ii for recracking or utilization else where. The overhead referred to is withdrawn through pipe it controlled by pressure reduction valve IS, from which it is discharged into pipe 26 controlled by valves 2! and 22, by which pipe it is discharged into the lower end of the vapor countercurrent contacting device 23, which in the specific case is an absorption tower. This maye be of the rectification tower type consisting of a vertical column spanned by horizontal trays equipped with bell caps and downfiow pipes, or a packed tower or a sieve tray tower. In either case, it is equipped for the downfiow of liquid and for the upflow of gas in countercurrent and intimate contact therewith. Sulfuric acid is inroduced into the upper end of 23 through pipe 2:; controlled by valve 25. As initially supplied through pipe 24 this sulfuric acid contains from 0.8 to 1.2 mols of ethylene per mol of sulfuric acid and is preferably at a temperature between 160 and 200 F. It flows downwardly within the device 23 in countercurrent contact with the as cending ethylene containing gas and is withdrawn from the base of 23 through pipe 25 controlled by valve 2'i into tank 28. Any gas which may be evolved from the absorbate in 28 may be vented through pipe 3! controlled by valve 32. The absorbate may be withdrawn from 23 through pipe 33 controlled by valve 34 for use in the usual way to generate ethyl alcohol or ethyl ether. A number of cooling coils diagrammatically indicated by '35 and 35 are provided upon the trays of 23 or at various liquid levels and these are preferably operated to maintain the temperature of the acid descending through the tower within F. of the temperature at which it is introduced through pipe 2d.

The amount of ethylene introduced through pipe 20 is stoichiometrically at least twice the amount which is absorbed within 23. Although the acid withdrawn from pipe 25 is not fully saturated, containing a maximum of 1.5 mols ethylene per mol of sulfuric acid, the rate of absorption falls off rapidly as this concentration is approached, making it of advantage to feed a substantial excess of ethylene upwardly through 23 while withdrawing an absorbate of this concentration from the base of 23. The use of a large excess of ethylene at this point favors the rapid reaction of ethylene with the acid up to a saturation approaching 1.5 mols of ethylene per mol of sulfuric acid, thereby resulting in efficient utilization of the absorption equipment. The residual gas in which the relative proportion of inert diluent is approximately twice that of the feed through pipe 28 is withdrawn through pipe 3'; controlled by pressure reduction valve 38. If the feed through pipe 29 is at a pressure of approximately 125 lbs. gauge, in order to maintain favorable absorption conditions in 23, the pressure reduction valve 38 will be set to maintain a back pressure of about 75 lbs. gauge, thereby resulting in the maintenance of an average pressure of approximately 100 lbs. gauge within 23. This is about the lowest limit in which I desire to operate. Preferably, the gas in reduced through pipe 20 is at a pressure of at least 225 lbs. gauge, thereby resulting in the maintenance of an average pressure within 23 of at least 200 lbs. gauge.

The overhead passing through pipe 3! and reduction valve 38 moves through pipe 39 into compressor, diagrammatically indicated by 4!, by which it is brought to a still higher pressure and delivered through pipe 52 controlled by valve 43 and through pipe id controlled by valve 45 into the base of liquid vapor countercurrent contacting device 65. This is similar to 23 in that it is constructed for the downward movement of a liquid countercurrent to an ascending stream of gas and, for this purpose, is equipped with horizontal trays spanning the tower, which trays carry bell caps and downflow pipes. A packed column or a sieve tray column may be similarly employed. Concentrated sulfuric acid may be introduced to the upper end of 36 through pipe 4! controlled by valve 18 and pipe 39 controlled by valve 58. The concentrated sulfuric acid is preferably introduced through pipe l? at a strength of 96 to 100% H2804. As withdrawn from the base of 46 through pipe controlled by valve 52, this acid will contain from 0.8 to 1.2 mols of ethylene per mol of sulfuric acid. Preferably the temperature of theacid moving downwardly within 26 is permitted to rise progressively to 160 to 200 F. and preferably 1'70 to 190 F. at the base. The acid, containing 0.8 to 1.2 mols of ethylene per mol of sulfuric acid, is withdrawn through pipe 5| controlled by valve 52 and a portion is transferred directly to 23 through pipe 53 and pressure reduction valve fi l'into pipe 24. The remainder is passed through cooler diagrammatically indicated by 55, by which it is reduced in temperature and thence moves from cooler 55 to pipe 56 controlled by valve 5! into pump 58, by which it is recirculated through pipe 59 controlled by valve 6! into the contacting device 46. The amount of acid recycled in this way through pump 58 may range from 2 to times by weight the amount of the fresh acid introduced through pipe 47. The temperature of the combined streams of acid entering the top of tower 56 ma range between 100 and 180 F.

Residual gas consisting principally of ethane is withdrawn from 46 through pipe 52 controlled by pressure reduction valve 63. The pressure drop in may be approximately lbs, resulting in the maintenance of an average pressure approximately 25 lbs. less than that for which reduction valve 53 is set. In this way the average pressure obtaining in G6 will be adjusted to at least 50% higher than the average pressure obtaining in 23 and preferably at least 100% higher. This results in optimum reaction conditions with a through-put that is extremely high for any particular equipment. In practice, the gas passing through pressure reduction valve 63 into pipe 64 will ordinarily be recycled into the feed to tower 3.

' pipe 42, I am able to absorb considerably more ethylene in :36 than would otherwise be the case, and since the gas in line 5 is already at a pressure at least equal to that obtaining in 42 and at a concentration of ethylene in the range of that obtaining in line 42, it is not necessary to recompress the gas "in pipe 6 nor is it necessary to rectify further that portion of the overhead from rectifyin column 3 to increase the concentration of ethylene therein.

The amount of gas introduced to 45 through pipe 6 is preferably sufficient to convey an amount of ethylene ranging from one-half to twice the amount absorbed in 23. As a result of this procedure the amount and rate of absorption in tower 3-6 is comparable to that obtaining in 23, The decreased partial pressure of the ethylene is compensated for by the absolute amount present, the increased total pressure, and the higher concentration of the sulfuric acid at this stage.

The foregoing description is for purposes of illustration and not of limitation and it is, therefore, my intention that the invention be limited only by the appended claims or their equivalents wherein I have endeavored to claim broadly all inherent novelty.

. I claim:

1. Process of absorbing ethylene in sulfuric acid to form a mixture of monoethyl and diet-hyl sulfates, which comprises maintaining a first liquid-vapor counter-current contacting device under an averagepressure of at least lbs. p. s. i. maintaining a second liquid-vapor countercurrent contacting device under an average pressure at least 50% greater than that obtaining in said first device, with series connections between said first and second devices for the transfer of vapor with intermediate compression from the upper end of said first device into the lower end of said second device, and for the transfer of acid from the lower end of said second device into the upper end of said first device, introducing sulfuric acid containing from 0.8-1.2 mols ethylene per mol H2804 into the upper end of said first device, conducting away from the lower end or said first device sulfuric acid containing from 1.3-4.5 mols ethylene per mol H2SO4, introducing a gas, the olefine content of which consists substantially exclusively of ethylene containing at least 30% by weight of ethylene and containing inert diluents, into the lower end of said first device, the amount of ethylene present in said gas being at least twice the amount which is absorbed in said first device, conducting residual gas containing ethylene and inert diluents from the top of said first device, compressing same and introducing the compressed gas into the lower end of said second device, introducing concentrated sulfuric acid into the upper end of said second device, conducting away from the base of said second device sulfuric acid containing from 0.84.2 mols ethylene per mol of sulfuric acid and introducing at least a part of the same into the top of said first device.

2. Process according to claim 1 in which the average pressure obtaining in said second device is at least 100% greater than the average pressure obtaining in said first device.

3. Process of absorbing ethylene in sulfuric acid to form a mixture of monoethyl and diethyl sulfates, which comprises maintaining a first liquid-vapor countercurrent contacting device under an average pressure of at least 200 lbs. p. s. i. g., maintaining a second liquid-vapor countercurrent contacting device under an average pressure at least 50% greater than that ohtaining in said first device, with series connections between said first and second devices for the transfer of vapor with intermediate c0mpression from the upper end of said first device into the lower end of said second device and for the transfer of ac d from the lower end of said second device into the upper end of said first device, introducing sulfuric acid containing from 0.8-1.2 mols ethylene per mol H2804 into the upper end of said first device, conducting away from the lower end of said first device sulfuric acid containing from 1.3-1.5 mols ethylene per mol I-IgSOr, introducing a gas, the olefine content of which consists substantially exclusively of ethylene containing at least 30% by weight of ethylene and containing inert diluents, into the lower end of said first device, the amount of ethylene present in said gas being at least twice the amount which is absorbed in said first device, conducting residual gas containing ethylene and inert diluents from the upper end of said first device, compressing same and introducing the compressed gas into the lower end of said second device, introducing concentrated sulfuric acid into the upper end of said second device, conducting away from the base of said second device sulfuric acid containing from 0.8-1.2 mols ethylene per mol of sulfuric acid and introducing at least a part of the same into the top of said first device.

4. Process according to claim 3 in which the average pressure obtaining in said second device is at least 100% greater than the average pressure obtaining in said first device.

5. Process of absorbing ethylene in sulfuric acid to form a mixture of monoethyl and diethyl sulfates, which comprises maintaining a first liquid-vapor countercurrent contacting device under an average pressure of at least 100 lbs. p. s. i. g., maintaining a second liquid-vapor countercurrent contacting device under an average pressure at least 50% greater than that obtaining in said first device, with series connections between said first and second devices for the transfer of vapor with intermediate compression from the upper end of said first device into the lower end of said second device and for the transfer of acid from the lower end of said second device into the upper end of said first de vice, introducing sulfuric acid containing from 0.8-1.2 mols ethylene per mol H2504 into the upper end of said first device, conducting away from the lower end of said first device sulfuric acid containing from 1.3-1.5 mols ethylene per mol H2504, introducing a gas containing at least 30% by weight of ethylene and containing inert diluents, into the lower end of said first device, the amount of ethylene present in said gas being at least twice the amount which is absorbed in said first device, conducting residual gas containing ethylene and inert diluents from the upper end of said first device, compressing same and introducing the compressed gas into the lower end of said second device, introducing concentrated sulfuric acid into the upper end of said second device, conducting away from the lower end of said second device sulfuric acid contain ing from 0.8-1.2 mols ethylene per mol of sulfuric acid, discharging a part of said last mentioned sulfuric acid into the upper end of said first device and combining the remainder with the concentrated sulfuric acid introduced into the upper end of said second device.

6. Process according to claim 5 in which the average pressure obtaining in said second drive is at least greater than the average pressure obtaining in said first device.

'7. Process of absorbing ethylene in sulfuric acid to form a mixture of monoethyl and diethyl sulfates, which comprises maintaining a first liquid-vapor countercurrent contacting device under an average pressure of at least 100 lbs. p; s. i. g., maintaining a second liquid-vapor countercurrent contacting device under an average pressure at least 50% greater than that obtaining in said first device, with series connections between said first and second devices for the transfer of vapor with intermediate compression from the top of said first device into the lower end of said second device and for the transfer of liquid from the lower end of said second device into the upper end of said first device, introducing sulfuric acid containing from 0.8-1.2 mols ethylene per mol H2804 at a predetermined temperature between and 200 E. into the top of said first device, abstracting heat from said sulfuric acid as it descends within said first device at a rate sumcient to maintain said redetermined temperature within :10 F., conducting away from the lower end of said first device sulfuric acid containing from 1.3-1.5 mols ethylene per mol H2SO4, introducing a gas, the olefine content of which consists substantially exclusively of ethylene containing at least 30% by weight of ethylene and containing inert diluents, into the lower end of said first device, the amount of ethylene present in said gas being at least twice the amount which is absorbed in said first device, conducting residual gas con taining ethylene and inert diluents from the upper end of said first device, compressing same and introducing the compressed gas into the lower end of said second device, introducing concentrated sulfuric acid at a temperature between 100 and 180 F. into the upper end of said second device, permitting the temperature of the descending stream of acid within said second device to rise exothermically to ISO-200 F. at the base thereof, conducting away from the base, of said second device sulfuric acid containing from 0.8-1.2 mols ethylene per mol of sulfuric acid and introducing at least a part of the same into the upper end of said first device.

8. Process of absorbing ethylene in sulfuric acid to form a mixture of monoethyl and diethyl sulfates, which comprises maintaining a first liquid-vapor countercurrent contacting device under an average pressure of at least 100 lbs. p. s. i. g., maintaining a second liquid-vapor countercurrent contacting device under an average pressure at least 50% greater than that obtaining in said first device, with series connections between said first and second devices for the transfer of vapor with intermediate compression from the upper end of said first device into the lower end of said second device and for the transfer of liquid from the lower end of said second device into the upper end of said first device, introducing sulfuric acid containing from 0.84.2 mols ethylene per mol H2304 at a predetermined temperature between 160 and 200 F. into the upper end of said first device, abstracting heat from said sulfuric acid as it descends wit -in said first device at a rate sumcient to maintain said predetermined temperature within :10" F., conducting away from the lower end of said first device sulfuric acid containing from 3-1.5 mols ethylene per mol HzSOi, introducing a gas, the clefine content of which consists substantially exclusively of ethylene containing at least 30% by weight of ethylene and containing inert diluents, into the lower end of said first device, the amount of ethylene present in said gas being at least twice. the amount which is absorbed in said first device, conducting residual gas containing ethylene and inert diluents from the upper end of said first device, compressing same and introducing the compressed gas into the lower end of said second device, introducing concentrated sulfuric acid at a temperature between l and 180 F. into the upper end of said second device, permitting the temperature of the descending stream of ac d within said second device to rise exothermically to 160- 00" F. at the base thereof, conducting away from the base of said second device sulfuric acid containing from 0.8-1.2 mols ethylene per mol of sulfuric acid, discharging a part of said last mentioned sulfuric acid into the upper end of said first device and combining the remainder with the concentrated sulfuric acid introduced into the upper end of said second device.

9. Process of absorbing ethylene in sulfuric acid to form a mixture of monoethyl and diethyl sulfates, which comprises maintaining a first liquid-vapor countercurrent contacting device under an average pressure of at least 100 lbs. p. s. i. g., maintaining a second liquid-vapor countercurrent contacting device under an average pressure at least 50% greater than that obtaining in said first device, with series con nections between said first and second devices for the transfer of vapor with intermediate compression from the upper end of said first device into the lower end of said second device, and for the transfer of acid from the lower end of said second device into the upper end of said first device, introducing sulfuric acid containing from 0.8-1.2 mols ethylene per mol H2SO4 into the upper end of said first device, rectifying a mixture of C-2 and C-3 hydrocarbons containing olefines to form a first product consisting predominantly of C-2s and containing ethylene, further rectifying this product to form a second product, the olefine content of which consists substantially exclusively of ethylene, containing at least by weight of ethylene and containing inert diluents, introducing such second prodnot into the lower end of said first device, conducting away from the lower end of said first device sulfuric acid containing from 1.3- .5 mols ethylene per mol H2804, the amount of ethylene present in said second product being at least twice the amount which is absorbed in said first device, conducting residual gas containing inert diluents from the upper end of said first device, compressing same to a pressure at least greater than that obtaining in said first device, combining gas so compressed with a part of said first product, introducing the combined gases into the lower end of said second liquid-vapor countercurrent contacting device, introducing concentrated sulfuric acid into the upper end of said second device, conducting away from the base of said second device sulfuric acid containing from 0.8-1.2 mols of ethylene per mol of sulfuric acid and introducing at least a part of the same into the top of said first device.

10. Process according to claim 9 in which the average pressure obtaining in said second device is at least greater than the average pres sure obtaining in said first device.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,365,044 Ellis Jan. 11, 1921 2,414,737 Heinrich Jan. 21, 1947 2,474,588 Morrell et al. June 28, 1949 2,497,959 Robey et a1. Feb. 21, 1950 2,545,161 Morrell et al a- Mar. 13, 1951 

1. PROCESS OF ABSORBING ETHYLENE IN SULFURIC ACID TO FORM A MXITURE OF MONOETHYL AND DIETHYL SULFATES, WHICH COMPRISES MAINTAINING A FIRST LIQUID-VAPOR COUNTER-CURRENT CONTACTING DEVICE UNDER AN AVERAGE PRESSURE OF AT LEAST 100 LBS. P.S.I.G., MAINTAINING A SECOND LIQUID-VAPOR COUNTERCURRENT CONTACTING DEVICE UNDER AN AVERAGE PRESSURE AT LEAST 50% GREATER THAN THAT OBTAINING IN SAID FIRST DEVICE, WITH SERIES CONNECTIONS BETWEEN SAID FIRST AND SECOND DEVICES FOR THE TRANSFER OF VAPOR WITH INTERMEDIATE COMPRESSION FROM THE UPPER END OF SAID FIRST DEVICES FOR THE LOWER END OF SAID SECOND DEVICES, AND FOR THE TRANSFER OF ACID FROM THE LOWER END OF SAID SECOND DEVICE INTO THE UPPER END OF SAID FIRST DEVICE, INTRODUCING SULFURIC ACID CONTAINING FROM 0.8-1.2 MOLS ETHYLENE PER MOL H2HO4 INTO THE UPPER END OF SAID FIRST DEVICE, CONDUCTING AWAY FROM THE LOWER END OF SAID FIRST DEVICE SULFURIC ACID CONTAINING FROM 1.3-1.5 MOLS ETHYLENE PER MOL H2SO4, INTRODUCING A GAS, THE OLEFINE CONTENT OF WHICH CONSISTS SUBSTANTIALLY EXCLUSIVELY OF ETHYLENE CONTAINING AT LEAST 30% BY WEIGHT OF ETHYLENE AND CONTAINING INERT DILUENTS, INTO THE LOWER END OF SAID FIRST DEVICE, THE AMOUNT OF ETHYLENE PRESENT IN SAID GAS BEING AT LEAST TWICE THE AMOUNG WHICH IS ABSORBED IN SAID FIRST DEVICES, CONDUCTING RESIDUAL GAS CONTAINING ETHYLENE AND INERT DILUENTS FROM THE TOP OF SAID FIRST DEVICE, COMPRESSING SAME AND INTRODUCING THE COMPRESSED GAS INTO THE LOWER END OF SAID SECOND DEVICE, INTRODUCING CONCENTRATED SULFURIC ACID INTO THE UPPER END OF SAID SECOND DEVICE, CONDUCTING AWAY FROM THE BASE OF SAID SECOND SULFURIC ACID CONTAINING FROM 0.8-1.2 MOLS ETHYLENE PER MOL OF SULFURIC ACID AND INTRODUCING AT LEAST A PART OF THE SAME INTO THE TOP OF SAID FIRST DEVICE. 